Ice cores hold secrets of what our planet was like millions of years ago, in bubbles preserving greenhouse gases from that time. A Princeton University -led team just revealed the date of ice from the oldest ice core we’ve ever dated, and it’s 2.7 million years old. Breaking the previous record by around 1.7 million years, the ice core could potentially help scientists determine what set off the ice ages . The ice core could help scientists understand more about our planet’s atmosphere millions of years ago. University of California, Berkeley geochemist David Shuster, who wasn’t part of the research, told Science Magazine, “This is the only sample of ancient Earth’s atmosphere that we have access to.” And the levels of carbon dioxide (CO2) in the planet’s atmosphere, according to research on the ice core, may surprise some: they didn’t exceed 300 parts per million. Related: Why scientists are transporting ice from a mountain in Bolivia to Antarctica There are models of our planet’s ancient climate which hinted there would need to be low levels of CO2 to trigger ice ages. But according to Science Magazine, proxies that came from the fossils of animals who dwelt in shallow oceans had hinted at higher CO2 levels. The proxies may need to be re-calibrated if the new ice core dating holds up. Researchers unearthed the ice core from what’s called blue ice in East Antarctica. Science Magazine explained that in blue ice areas, glacial flow has allowed some ancient ice to come up to the surface. As a result, scientists don’t need to drill as deep to obtain old ice core samples in blue ice. The Princeton team hopes to extract still more ice cores from there and geochemist Ed Brook of Oregon State University , who was part of the team, said they could potentially find ice that dates back five million years. Princeton University graduate student Yuzhen Yan presented the research at the Goldschmidt Conference in Paris earlier this month. Scientists from institutions in California and Maine also made contributions. Via Science Magazine Images via Yuzhen Yan, Department of Geosciences